EPRI conducted its study at its power utilization lab in Knoxville, Tennessee. The research showed that an "iPad consumes less than 12 kWh of electricity over the course of a year, based on a full charge every other day. By comparison, a plasma 42" television consumes 358 kWh of electricity a year."

Based on an average cost of electricity, the annual cost of keeping that iPad alive is about US$1.36 per year -- the actual cost would vary depending on what your local electric utility charges per kWh. EPRI did the same study for an iPhone 3G and found that it consumed 2.2 kWh of electricity every year, or about $0.25 annually.

Of course, there's more than one iPad on the planet, so EPRI calculated the energy impact of all of the iPads sold and came up with a number of 590 gigawatt hours (GWh). According to EPRI, "In a scenario where the number of iPads tripled over the next two years, the energy required would be nearly equivalent to two 250-megawatt (MW) power plants operating at a 50 percent utilization rate. A quadrupling of sales in two years would require energy generated by three 250-MW power plants."

Lest you think your iPad is an energy hog, consider a comparison to a laptop. EPRI found that laptops (no model specified) feast on about 72.3 kWh of electricity per year at an average cost of $8.31. That's six times the energy impact of your iPad.